1. Field of the Preferred Embodiment(s)
This invention generally relates to position sensing and to a position sensor which is compact, durable and precise. More specifically, the invention relates to a non-contacting 360 degree position sensor.
2. Description of the Related Art
Position sensing is used to allow an electrical circuit to gain information about an event or a continuously varying condition. There are a variety of known techniques for angular position sensing. For example, optical, electrical, electrostatic, and magnetic fields are all used in a sensor to measure position. There are many known sensors such as resistive contacting networks, inductively coupled ratio sensors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, and electrostatic ratio detectors.
There are many applications for sensors, and a wide variety of technologies to fill these needs. Each of these technologies offers a unique set of advantages and limitations. Of these technologies, magnetic sensing is known to have a unique combination of long life components and excellent resistance to contaminants.
Regardless of the arrangement and method for changing the field about the sensor, the magnetic circuit faces several obstacles which have not been overcome. Movement of the sensor relative to the gap as a result of bearing play will lead to a variation in field strength measured by the sensor. This effect is particularly pronounced in Hall effect, magneto-resistive and other similar sensors, where the sensor is sensitive about a single axis and insensitive to another axis magnetic field.
Another problem with the prior art magnetic sensors is that eddy current effects occur when a magnet is held stationary with respect to a rotating ferromagnetic material. For example, in a variable reluctance sensor for a crankshaft sensor, a stationary magnet is located near the rotating teeth of a steel gear. The eddy current effects cause the signal strength generated by the sensor to be reduced.
Description of Related Art
Examples of patents related to the present invention are as follows, wherein each patent is herein incorporated by reference for related and supporting teachings:
U.S. Pat. No. 3,112,464 is a hall effect translating device.
U.S. Pat. No. 4,142,153 is a tachometer for measuring speed and direction of shaft rotation with a single sensing element.
U.S. Pat. No. 4,293,837 is a hall effect potentiometer.
U.S. Pat. No. 4,570,118, is an angular position transducer including permanent magnets and hall effect device.
U.S. Pat. No. 4,726,338 is a device for controlling internal combustion engines.
U.S. Pat. No. 4,744,343 is a device for controlling an internal combustion engine.
U.S. Pat. No. 4,848,298 is a device for controlling internal combustion engine.
U.S. Pat. No. 4,942,394 is a hall effect encoder apparatus.
U.S. Pat. No. 5,055,781, is a rotational angle detecting sensor having a plurality of magnetoresistive elements located in a uniform magnetic field.
U.S. Pat. No. 5,115,239 is a magnetic absolute position encoder with an undulating track.
U.S. Pat. No. 5,159,268 is a rotational position sensor with a hall effect device and shaped magnet.
U.S. Pat. No. 5,258,735 is a multi-pole composite magnet used in a magnetic encoder.
U.S. Pat. No. 5,313,159 is a magnetic encoder with composite magnet.
U.S. Pat. No. 5,712,561 is a field strength position sensor with improved bearing tolerance in a reduced space.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicants' acknowledged duty of candor in disclosing information that may be pertinent in the examination of this application.
Problems with the Prior Art
There are several problems that exist with the prior art that are addressed by the preferred embodiment. One problem with magnetic position sensors is how to provide a continuous output signal representative of the angular position of a continuously rotating object. Prior art sensors used individual magnets arrayed around a rotating object to give an indication of several individual discrete angular positions. For example, a rotating gear using symmetrically spaced teeth which rotate near a fixed magnet as in a variable reluctance sensor. Another prior art technique which has the same problem is an optical comparator which decodes the position of symmetrically spaced slots on a rotating disk.
Another problem is that the prior art sensor outputs have not been linear. In many control applications, it is necessary to have a linear output to provide the precise control needed in many applications. The prior art sensors have been single point detectors and/or accumulators.
This and other problems will be solved by the preferred embodiments of the invention. A review of the specification, drawings, and claims will more clearly teach a skilled artisan of other problems that are solved by the preferred embodiments.